Focused and directed laser beams are commonly used for a variety of processes, such as drilling of blind, through and micro-vias, laser imaging, dicing of substrates and modification or customization of integrated circuits, drilling, cutting, and selective material removal and other complex machining and micro-machining operations involving materials such as metals, polymers, integrated circuits, substrates, ceramics and other materials. Such processes have become very complex, often involving the concurrent or sequential of use of single or multiple lasers or multiple types of lasers, such as visible, infra-red (IR) and ultraviolet (UV) lasers, in concurrent or sequential operations. In generally all such laser processes, however, the general object of a laser system is to controllably and reliably direct, focus and concentrate the energy of one or more laser beans to converge each beam at a desired spot or to image an aperture area of a laser beam onto the surface of an object.
One of the major requirements for use of such systems is the alignment of the elements of the optical system to safely deliver a correctly focus and shaped laser beam at the intended target, which typically requires the individual and joint alignment of each optical element in the system. Stated simply, the alignment process requires that the aligner determine for each optical element, such as a mirror, where the beam strikes the optically functional area of the element. The aligner should also preferably be able to determine the shape or pattern of the beam at that point and possibly the relative power of the beam at that point.
This problem further compounded in that the laser beams generated in many laser beam delivery systems, such as ablation systems, are comprised of “invisible” or “non-visible”, radiation, that is, radiation that is not visible to the unaided human eye. Such non-visible radiation may include, for example, UV (ultraviolet) radiation or infrared (IR) radiation, and may also include beams comprised of radiation at wavelengths that are in or near the visible spectrum but that because of other characteristics, such as power and beam width, are difficult to see and are thereby effectively “non-visible”.
Such beams are also often of relatively high power levels, and are thereby a significant hazard to the eyes of the aligner and user of the system and to any others that may stray into the path of the beam as the aligner, user or bystander may be unaware of a hazard from the beam until damage has been inflicted. This problem is further compounded because it is effectively impossible to align a non-visible radiation system without optical assistance, thereby placing the aligner's eye or eyes in the danger zone.
For these reasons, UV systems of the prior art were typically aligned by inserting a piece of white paper into the general and assumed path of the UV beam. White paper typically fluoresces when irradiated with UV radiation, so that a fluorescent spot will appear on the paper indicated the position of the beam, if the paper is in the path of the beam. This method has a number of disadvantages, however. One is that the aligner is exposed to significant levels of scatter radiation, that is, UV radiation reflected from the surface of the paper, which can cause a “sun burn” type of injury or even photothalmia, which is effectively a sunburn of the eye tissues. The other problem is that the paper effectively blocks the path of the beam, so that if a mirror, for example, is behind the paper, the location at which the beam strikes the surface of the mirror must be estimated from the location at which the beam strikes the paper. This problem becomes more severe, of course, the greater the distance between the paper and the surface of the mirror and can be reduced by placing the paper closely on the surface of the mirror, which may be a problem in itself due to mechanical constraints and the possibility of smearing the surface of the mirror. Yet another problem with this method is that the laser beam sometimes “burns” the paper, resulting in the deposit of contaminates on the mirror or on other optical elements of the system.
There are also a number of related problems that repeatedly appear problems in such laser micro-machining operations. One problem, for example, is determining the position and orientation of the work surface, that is, the surface to be machined, relative to some known point in order to adjust and control, for example, the location, focus and depth of the laser beams to obtain the desired machining operation. In a further example, it is often necessary to determine the “flatness” of a work surface, that is, and for example, whether the work surface is tilted with respect to the axis of the coordinate system axes of the laser beam or is curved or otherwise warped away from being both “flat” and perpendicular to the intended axis of the laser beam. Information regarding the“flatness” of a work surface can be used to adjust the orientation of the work surface with regard to the machining beam, or may be mapped to control the machining beam accordingly to obtain the optimum results.
Prior art laser displacement measurement systems relying on a triangulation method of determining distance. They use a single beam directed at an angle that when retro-reflected projects onto a single linear photo detector. This type of detector needs to be calibrated when installed and only provide one data point. If this type of unit is removed and re-installed it requires a complete re-calibration. The prior art systems do not allow for the calculation of flatness, to accomplish that they need to be indexed across a surface or scanned across a surface to sample three or more points, at which point a secondary CPU would need to calculate off line what the flatness is. These types of systems are very costly.
When the prior art systems are used in conjunction with automated assembly systems they lack the ability to provide closed loop feedback to positioning systems. The prior art systems require multiple sampling series to determine an objects position, then verify its position once the object has been correctly placed or adjusted using automated motion devices and actuators.
Prior art systems also lack the ability to use alternative wavelength of laser light including UV and various IR wavelengths. This limits the use of these types of laser triangulation devices to material which can reflect the wavelength being used.
The present invention provides a solution to these and related problems of the prior art